This invention relates generally to an apparatus for controlling the propulsion of a paver and, more particularly, to an apparatus for controlling the propulsion of a paver utilizing a microprocessor based system.
Asphalt pavers include a hopper for receiving paving material and a conveyor system for transferring the paving material from the hopper for discharging on the roadbed. Screw augers spread the material on the roadbed in front of a floating screed, which is connected to the paving machine by pivoting tow or draft arms. The screed functions to format and compact the paving material distributed by the augers, ideally leaving the finished road with a uniform, smooth surface.
Such machines may be propelled by using several types of ground engaging traction devices, e.g., rubber wheels or endless metal (or rubber) belts that are disposed on opposite sides of the machine. The steering of a belted type machine is carried out by creating a differential speed between the oppositely disposed ground engaging traction devices.
Unfortunately, such machines that use differential speed steering develop several problems. Once such problem is that the machine does not track straight when it is desired that it do so. Another problem is that the desired turn radius of the machine varies with the travel speed of the machine. Thus, it becomes difficult for the operator to control the machine with a high degree of consistencyxe2x80x94a crucial element for asphalt paving.
Another problem of typical pavers is the reliance on analog circuitry to control the propulsion. As is well known, analog circuitry is inflexible and does not allow for customization of machine performance as does programmable digital circuitry.
Finally, another problem of many pavers is the use of the mechanical braking system to stop the machine. Such mechanical braking system are typically used in conjunction with the hydrostatic drive system. However, because rarely does the mechanical braking system act in concert with the hydraulic system, abrupt breaking or wearing of the mechanical brakes may occur.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, an apparatus for controlling the propulsion of a machine having a hydrostatic system that drives a plurality of ground engaging traction devices is disclosed. An electronic controller receives a desired travel speed signal and a steering angle signal, determines a desired rotational speed of the orthogonal engaging traction devices to steer the machine at the desired steering angle, and produces command signals indicative of the desired rotational speeds. An electrohydraulic device receives command signals and responsively controls the speed of the ground engaging traction devices to the desired speed to cause the machine to steer at a desired turning radius that is independent to the actual speed of machine travel.